1. Field of the Invention
The present invention relates generally to legacy data processing systems employing complex Input/Output processing facilities and more particularly relates to the use of such Input/Output facilities to conveniently interface with a variety of peripheral devices employing emulation and a Small Computer Systems Interface (SCSI).
2. Description of the Prior Art
A great many large organizations have enterprise-based legacy data processing systems which are integral to their very process of doing business. Embedded within such legacy data processing systems are various legacy software programs, many of which have been operating literally without any attention for a large number of years. Thus, as data processing technology has moved forward by leaps and bounds, some of the most basic and most important hardware and software elements have remained constant.
In many cases, new and upwardly compatible hardware may be added to the legacy data processing system to enhance the total throughput and provide additional functionality. In most cases, however, the most fundamental legacy software, which provides the actual logic for the business operation, remains unmodified.
Therefore, there remains a constant tension between the desire to update legacy systems with more cost effective hardware and software components and the desire to avoid costly and unreliable modifications to those system elements which are have been satisfactorily operational for extended periods of time. The most straightforward method of effecting upgrades is to couple the new hardware and software to the legacy data base management system and modify those system components requiring changes to accomplish integration. In many cases, this can mean changes to the operating system, system software, and multiple application software packages, in addition to the necessary hardware changes.
Unfortunately, this approach can be very costly, as well as, providing an adverse impact upon system reliability until all changes have been thoroughly debugged. Furthermore, this approach tends to render the system unusable for unacceptable periods of time.
The present invention overcomes the problems found in the prior art by providing a method of and apparatus for effectively and efficiently connecting a peripheral device of relatively new design to a legacy data base management system. In accordance with the preferred mode of the present invention, the legacy data processing system is a Model 2200 mainframe system available from Unisys Corporation. The newly designed device to be added is a Digital Video Drive (DVD).
The key to the approach of the present invention is emulation. In accordance with this technique, the legacy data processing system appears to interface with an older type of peripheral device for which it has been previously configured. Similarly, the new peripheral device appears to interface with an input/output facility specifically created for the newer device. The emulation is accomplished by software located within the input/output function, which integrates the new device (i.e., DVD in the preferred embodiment) with the preexisting Small Computer Systems Interface (SCSI) tape interface of the Model 220 legacy data processing system.
The novel aspects of the invention involve the basic Input/Output (I/O) system consisting of a device (e.g., DVD), a control unit, a channel, and I/O Processor, memory, and an Instruction Process (IP). In particular the invention focuses upon the control unit, channel, and I/O Processor.
The device contains a control unit that is hooked to the channel. For a SCSI tape drive, both a control unit and a device driver are integrated. This peripheral is then connected to a channel.
The channel is a PCI bus card. The card contains the micro code that interfaces with the peripheral control unit. When an operating system needs to communicate with a new channel it is sometimes necessary to interface with a new communication protocol. For example SCSI and BMC use different protocols.
The channel is connected to an I/O Processor. In the preferred mode, the I/O Processor includes the Commodity Operating System, the Commodity Application Software, and the Emulated Peripheral Software, available from the Unisys Corporation.
It is the Emulated Peripheral Software, which is the heart of the present invention. This software allows the mainframe operating system to treat the emulated peripheral (e.g., DVD) as an already existing peripheral type. As a result, there is no longer a need for the operating system to perform a large adaptation or system modification to recognize the new device, nor does the channel need to be changed. The elimination of the large adapt significantly reduces the amount of software that needs to be written as well as frees up the operating system""s resources.
Essentially, when a user implements a new device such as a DVD player and/or a new set of files such as a new DVD, the operating system does not read this as requiring a change in software or a change in the channel. Instead, the emulated peripheral software hides the new device, and allows the device to be integrated into the system with minimal interruption.
More specifically, the OS 2200 operating system, available from Unisys Corporation, supports the BMC, ISI, SCSI, and SBGCON protocols. Also each control unit has unique commands and statuses for each protocol. So an operating system adapt for a new peripheral may require an entire channel adapt and will always require a control unit adapt. The present invention adds another piece of software that interfaces with a Microsoft operating system controlled DVD and eliminates the channel and control unit adapts.